Design goals

The kit that I bought in 2017 has been great for drilling (and milling) PCBs, but it had a number of flaws with it, the main one being the spindle doesn't run that fast (about 1200RPM) - but it's also a bit small.

Since the spindle is quite small, replacing it will be tricky - however, I decided that I may as well make a bigger one so that I could do much more.

Spindle

The spindle wasn't suitable for perspex or aluminium - although I did have a go with perspex on the smaller machine. Of the four pieces it was attempting to mill from a single sheet, only one came out close to what I wanted.

Bed size

One of the things I've always wanted to do is mill front panels - and a 4U panel is the largest that I envisaged. This meant a useable working area of around 500mm x 180mm.

Layout

My 1st and 2nd CNC machines had a static bed, with a frame that moved over all three axes.

The problem with the 1st one was that it was way too big, and there was too much 'bounce' when the machine stopped. This was repeated on the 2nd machine until I fitted a second ball screw down the Y axis using a second stepper motor (with driver) that moved in synchrony with the other one. This meant that both sides of the Y axis were tied to each other.

For the 4th machine, I used the same designed as the 3rd, where the frame holds the X and Z axes above the bed, which moves along the Y axis. This is identical to the small CNC machine that I've been using for PCB drilling, and is nice in that the Z axis only moves in the X axis, and isn't affected by Y axis movement. The bed is also contained within the frame.

Purchasing

I opted for a 100V spindle with a controller. This can go up to just over 10,000RPM, which means I should be able to do perspex and even aluminium.

I bought a pair of 700mm long ACME screws for the X axis, and 500mm long ACME screw for the Y axis. The Z axis wasn't that important, so I used a 200mm long ACME screw for this.